The work described in this proposal will be done with the broad, long-term objective of delineating the mechanisms by which dominant mutations provoke the development of a specific class of neurodegenerative diseases called inherited prion diseases. These diseases are unique among human illnesses because they are simultaneously inherited and yet transmissible to experimental animals. Because they are transmissible they hold important research advantages over other dominantly inherited neurodegenerative diseases; they can be modelled in experimental animals and in tissue culture. Furthermore, a missense variant of the prion protein (Prp), the major macromolecule involved in the pathogenesis and transmission of prion diseases, was recently shown to be genetically linked to Gerstmann-Straussler syndrome (GSS), a form of inherited prion disease. The human PRP gene (PRNP) is thus an obvious candidate gene to study for effects of mutations on prion disease phenotypes in humans and on de novo prion generation in animals and cultured cells. The demonstration of a causal relationship between mutations in PRNP and disease would constitute the first example of dominant gene expression resulting in neurodegenerative disease. Furthermore, it would constitute incontrovertible evidence that prions can be generated from PrP alone, obviating the need to invoke an abetting, but furtive nucleic acid, and thus firmly establish prions as novel biologic agents. The research entailed in these studies will specifically involve 1) completing a catalogue of PRNP mutations in inherited prion diseases and 2) developing biologic assays of PRNP mutants. Based upon clinical and pathologic criteria at least four forms of inherited prion diseases can be deciphered. A codon 102 proline to leucine variant of PrP has been found to correspond to one form of disease, ataxic GSS. Sequences of PRNP from patients with other forms of inherited prion diseases will be determined in order to learn whether specific PrP variants or sets of PrP variants correspond to other forms of disease. Such information would not only support the hypothesis that PRNP mutations cause inherited prion diseases, but would also direct attention towards regions of PrP likely to be involved in generating disease. The effects of these mutations will be assayed in cultured cells transfected with recombinant PrP mutants and in mice containing mutant PrP transgenes.